Project Summary Olfactory neural circuits generate tens of thousands of distinct perceptions and influence innate behaviors, such as feeding, and in many mammals, pheromone responses such as fighting and mating. Mammals have two principal olfactory tissues: the main olfactory epithelium and the vomeronasal organ, each of which contains large families of dedicated sensory receptors and activates distinct neuronal circuits. We recently identified two non-canonical families of mammalian chemosensory receptors that are distinct from previously described odorant and vomeronasal receptors. In this proposal, we aim to understand the evolution, cellular organization, and chemoreceptive fields of these novel sensory receptors, to provide additional insight into the molecular mechanisms that underlie olfaction in mammals.